While template driven polymerization processes have received much scrutiny in the past two decades, little is known about the non-template dependent enzymes that make homopolymers from phosphate (polyphosphate kinase), isopentenylpyrophosphate (rubber synthase), a variety of sugars (starch, glycogen and heparin synthases) and 3-hydroxyalkanoate thioesters (polyhydroxyalkanoate (PHA) synthases.) Our studies will focus on the Class I and III PHA synthases (from Rastonia eutropha and Chromatium vinosum, respectively), which make polyhydroxybutyrates (PHB) and polyhydroxyvalerates (PHV). We hope to understand the detail mechanism of PHA formation: the priming and/or initiation steps, the elongation steps and the termination steps, that is, the factors that determine polymer size and polydispersity, both in vitro and in vivo. Our studies will also focus on understanding PHA homeostasis in vivo: specifically the roles of the phasin (PhaP), the PHA depolymerases (PhaZ1 and PhaZ2), and the putative transcription factor (PhaR). These in vitro and in vivo studies will lead to the improved understanding of the factors that determine polymer composition, size, and polydispersity and could lead to the development of biodegradable materials with novel properties of commercial interest for bulk and specialty plastics.